Environmental Assis for Orono Substation Expansion

Home Browse Search

Table 7: Calculated Transmission Line Audible Noise Levels (3.28 feet above ground) Source: Xcel Energy, June 7, 2011; Xcel Energy, personal communication, November 7, 2011. Calculations were performed using the EPRI Enviro software and the BPA standard method of calculation. Substation Noise Noise associated with substations includes the operation of transformers and switchgear. The transformers produce a constant low -frequency humming noise while the switchgear produces an impulsive or short duration noise during infrequent activation of the circuit breakers. The distance between the Xcel Orono Substation property boundary to nearby homes are approximately 180 feet to the south, across County Road 6, and approximately 270 feet to the west (Xcel Energy, personal communication, October 13). Xcel Energy proposes to install a 28MVA distribution transformer that is currently in storage. Future plans anticipate upgrading the 28MVA transformer to 50MVA and eventually adding a second 50 MVA transformer; the date of the upgrade and addition is dependent upon customer load growth demands (Xcel Energy, personal communication, November 21, 2011). Xcel Energy is currently conducting a noise assessment of the Orono Substation site. Because no noise level data is available from Xcel Energy records or from the manufacturer of this transformer Xcel Energy is using an assumed 75 to 78 dBA noise level range at the transformer location. Mitigation Measures HVTL route permits require compliance with state noise standards established by the MPCA. The Project will be designed and constructed to comply with state noise standards established by MPCA during operation of the transmission line and substation. Construction activities would also need to comply with MPCA noise standards. Construction work would generally be limited to daytime hours, between 7 a.m. and 10 p.m on weekdays. Occasionally there may be construction outside of these hours or on a weekend if it becomes necessary to work around customer schedules or line outages. Heavy equipment would be equipped with sound attenuation devices such as mufflers to minimize noise levels (Xcel Energy, personal communication, November 14, 2011). Environmental Assessment PUC Docket E002/TL-11-223 Page 28 Audible Noise Levels at Edge of Right -of -Way Structure Type (dBA) L5 L5o Single Pole Vertical Configuration with Post 14.5 11.0 Insulators, 115 kV Single -Circuit Single Pole Davit Arm 115 kV / 115 kV Double -Circuit 23.3 19.8 Single Pole Davit Arm 115 kV/ 115kV Double Circuit with Distribution Under Build 23.3 19.8 Single Pole, Cross Arm, Y -Frame Structure 115 15.8 12.3 kV Single -Circuit Source: Xcel Energy, June 7, 2011; Xcel Energy, personal communication, November 7, 2011. Calculations were performed using the EPRI Enviro software and the BPA standard method of calculation. Substation Noise Noise associated with substations includes the operation of transformers and switchgear. The transformers produce a constant low -frequency humming noise while the switchgear produces an impulsive or short duration noise during infrequent activation of the circuit breakers. The distance between the Xcel Orono Substation property boundary to nearby homes are approximately 180 feet to the south, across County Road 6, and approximately 270 feet to the west (Xcel Energy, personal communication, October 13). Xcel Energy proposes to install a 28MVA distribution transformer that is currently in storage. Future plans anticipate upgrading the 28MVA transformer to 50MVA and eventually adding a second 50 MVA transformer; the date of the upgrade and addition is dependent upon customer load growth demands (Xcel Energy, personal communication, November 21, 2011). Xcel Energy is currently conducting a noise assessment of the Orono Substation site. Because no noise level data is available from Xcel Energy records or from the manufacturer of this transformer Xcel Energy is using an assumed 75 to 78 dBA noise level range at the transformer location. Mitigation Measures HVTL route permits require compliance with state noise standards established by the MPCA. The Project will be designed and constructed to comply with state noise standards established by MPCA during operation of the transmission line and substation. Construction activities would also need to comply with MPCA noise standards. Construction work would generally be limited to daytime hours, between 7 a.m. and 10 p.m on weekdays. Occasionally there may be construction outside of these hours or on a weekend if it becomes necessary to work around customer schedules or line outages. Heavy equipment would be equipped with sound attenuation devices such as mufflers to minimize noise levels (Xcel Energy, personal communication, November 14, 2011). Environmental Assessment PUC Docket E002/TL-11-223 Page 28